This invention relates to stud welding which is a form of electric arc welding. In practice, a metal stud is loaded into an electrically energizable collet, which is usually situated in the barrel of a stud welding tool, and is then grasped and positioned over an attachment site on a work area or work piece. When the tool is energized, an arc is created between the distal end of the stud and the attachment site on the metal work piece. The arc melts both the distal tip of the stud and creates a molten pool at the area of attachment on the work piece. A timing device in the tool determines the duration of the arc and, when the arc is completed, the tool plunges the stud into the molten pool at the area of attachment, creating a weldment to the work piece.
One aspect of stud welding is ensuring proper setting of the plunge on the stud weld tool. The plunge is the amount of the weld stud protruding past the end of the plunge stop. The amount of plunge effects two different parameters. First, it affects the amount of preload on the main weld spring. More plunge equates to more preload, which results in shorter weld times. Although adjusting the amount of plunge is not the primary means of adjusting weld timing, the timing effect does need to be considered. The second effect, is to control the pressure and/or depth used in joining the melted base material to the melted face of the fastener, with more plunge resulting in more pressure or depth used in joining the melted surfaces together.
In one currently utilized plunge adjustment method, a leg and foot assembly is mounted to the exterior of the stud welding tool. The mounting feature can be an aluminum face plate on the stud welding tool having holes through which the legs of the assembly are slidably attached. Set screws can be used to lock the legs in place at a desired setting. With this type of plunge adjustment configuration, the plunge can be adjusted by sliding the assembly forward or rearward along the tool relative to the weld stud. Sliding the assembly is typically accomplished by loosening the set screws, manually sliding the assembly until the line up looks to be “right” then retightening the set screws. The leg and foot assembly plunge adjustment method is, at best, an imprecise adjustment method. Furthermore, this adjustment method requires the use of extra tools for loosening and tightening the set screws, and results in increased procedure time.
A second known method of adjusting plunge, though being less common, is to adjust the weld stud collet depth stop. This adjustment method is not convenient because it requires removal of the collet which typically requires the use of extra tools.
Further, the weld parameters are impacted by other mechanical settings controlled by the weld tool. For example, another aspect of stud welding relates to proper setting of the timing device in the tool that determines the duration, or length, of the arc. Various stud welding tools control this welding parameter in different ways. For example, spring compression is used in contact capacitor discharge (CD) welding, gap distance is used in gap CD welding, and solenoid lift distance is used in drawn arc stud welding.
In contact CD welding, the weld fastener generally starts in contact with work piece and all components are not moving at the start of the weld sequence. Contact CD welding utilizes spring pressure to control the arc timing. The more compressed the main weld spring, the faster the tool drives the weld fastener into the weld puddle. One common way of adjusting the spring pressure is to change the spring within the weld tool, such as changing to a higher fixed rate spring. Another common way of adjusting the spring pressure is to utilize a simple screw mechanism that increases or decreases the spring preload.
For gap CD welding, the weld fastener starts the weld sequence raised above the work piece. This distance that the fastener is raised above the work piece is called the gap distance. Once the weld cycle is initiated, the weld fastener accelerates toward the work piece. By varying the initial gap distance, the amount of time the weld fastener has to accelerate changes, which changes the speed at which the weld fastener contacts the work piece and proceeds into the weld puddle.
Finally, in drawn arc welding, the solenoid lifts the weld fastener away from the work piece. This lift distance controls the length of the arc that can be established. Longer arcs generate higher temperature as there is more resistance in a longer arc. Changing the solenoid position changes the lift distance, thus effecting the arc length.